[PATCH 0/4] arm64: topology: CPU topology support

[PATCH 0/4] arm64: topology: CPU topology support

[Mark Brown]

This revision of the series places any otherwise unmapped CPUs into a
cluster in order to avoid confusing the scheduler if no topology
information is provided.  This means that we should never bring up a CPU
with no topology information so while the warning is still present and
has been upgraded it should never triger unless there is a genuine bug
(as opposed to missing information).

Mark Brown (4):
      arm64: topology: Implement basic CPU topology support
      arm64: topology: Add support for topology DT bindings
      arm64: topology: Tell the scheduler about the relative power of cores
      arm64: topology: Provide relative power numbers for cores

 arch/arm64/Kconfig                |  24 +++
 arch/arm64/include/asm/topology.h |  39 ++++
 arch/arm64/kernel/Makefile        |   1 +
 arch/arm64/kernel/smp.c           |  11 ++
 arch/arm64/kernel/topology.c      | 388 ++++++++++++++++++++++++++++++++++++++
 5 files changed, 463 insertions(+)

[PATCH 1/4] arm64: topology: Implement basic CPU topology support

[Mark Brown]

From: Mark Brown <broonie@linaro.org>

Add basic CPU topology support to arm64, based on the existing pre-v8
code and some work done by Mark Hambleton.  This patch does not
implement any topology discovery support since that should be based on
information from firmware, it merely implements the scaffolding for
integration of topology support in the architecture.

No locking of the topology data is done since it is only modified during
CPU bringup with external serialisation from the SMP code.

The goal is to separate the architecture hookup for providing topology
information from the DT parsing in order to ease review and avoid
blocking the architecture code (which will be built on by other work)
with the DT code review by providing something simple and basic.

A following patch will implement support for parsing the DT topology
bindings for ARM, similar patches will be needed for ACPI.

Signed-off-by: Mark Brown <broonie@linaro.org>
---
 arch/arm64/Kconfig                |  24 +++++++++
 arch/arm64/include/asm/topology.h |  39 +++++++++++++++
 arch/arm64/kernel/Makefile        |   1 +
 arch/arm64/kernel/smp.c           |  11 ++++
 arch/arm64/kernel/topology.c      | 102 ++++++++++++++++++++++++++++++++++++++
 5 files changed, 177 insertions(+)
 create mode 100644 arch/arm64/include/asm/topology.h
 create mode 100644 arch/arm64/kernel/topology.c

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 27bbcfc..fea7b47 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -164,6 +164,30 @@ config SMP
 
 	  If you don't know what to do here, say N.
 
+config CPU_TOPOLOGY
+	bool "Support CPU topology definition"
+	depends on SMP
+	default y
+	help
+	  Support CPU topology definition, based on configuration
+	  provided by the firmware.
+
+config SCHED_MC
+	bool "Multi-core scheduler support"
+	depends on CPU_TOPOLOGY
+	help
+	  Multi-core scheduler support improves the CPU scheduler's decision
+	  making when dealing with multi-core CPU chips at a cost of slightly
+	  increased overhead in some places. If unsure say N here.
+
+config SCHED_SMT
+	bool "SMT scheduler support"
+	depends on CPU_TOPOLOGY
+	help
+	  Improves the CPU scheduler's decision making when dealing with
+	  MultiThreading at a cost of slightly increased overhead in some
+	  places. If unsure say N here.
+
 config NR_CPUS
 	int "Maximum number of CPUs (2-32)"
 	range 2 32
diff --git a/arch/arm64/include/asm/topology.h b/arch/arm64/include/asm/topology.h
new file mode 100644
index 0000000..c8a47e8
--- /dev/null
+++ b/arch/arm64/include/asm/topology.h
@@ -0,0 +1,39 @@
+#ifndef __ASM_TOPOLOGY_H
+#define __ASM_TOPOLOGY_H
+
+#ifdef CONFIG_CPU_TOPOLOGY
+
+#include <linux/cpumask.h>
+
+struct cpu_topology {
+	int thread_id;
+	int core_id;
+	int cluster_id;
+	cpumask_t thread_sibling;
+	cpumask_t core_sibling;
+};
+
+extern struct cpu_topology cpu_topology[NR_CPUS];
+
+#define topology_physical_package_id(cpu)	(cpu_topology[cpu].cluster_id)
+#define topology_core_id(cpu)		(cpu_topology[cpu].core_id)
+#define topology_core_cpumask(cpu)	(&cpu_topology[cpu].core_sibling)
+#define topology_thread_cpumask(cpu)	(&cpu_topology[cpu].thread_sibling)
+
+#define mc_capable()	(cpu_topology[0].cluster_id != -1)
+#define smt_capable()	(cpu_topology[0].thread_id != -1)
+
+void init_cpu_topology(void);
+void store_cpu_topology(unsigned int cpuid);
+const struct cpumask *cpu_coregroup_mask(int cpu);
+
+#else
+
+static inline void init_cpu_topology(void) { }
+static inline void store_cpu_topology(unsigned int cpuid) { }
+
+#endif
+
+#include <asm-generic/topology.h>
+
+#endif /* _ASM_ARM_TOPOLOGY_H */
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 2d4554b..252b621 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -20,6 +20,7 @@ arm64-obj-$(CONFIG_HAVE_HW_BREAKPOINT)+= hw_breakpoint.o
 arm64-obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
 arm64-obj-$(CONFIG_ARM64_CPU_SUSPEND)	+= sleep.o suspend.o
 arm64-obj-$(CONFIG_JUMP_LABEL)		+= jump_label.o
+arm64-obj-$(CONFIG_CPU_TOPOLOGY)	+= topology.o
 
 obj-y					+= $(arm64-obj-y) vdso/
 obj-m					+= $(arm64-obj-m)
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 7cfb92a..9660750 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -114,6 +114,11 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 	return ret;
 }
 
+static void smp_store_cpu_info(unsigned int cpuid)
+{
+	store_cpu_topology(cpuid);
+}
+
 /*
  * This is the secondary CPU boot entry.  We're using this CPUs
  * idle thread stack, but a set of temporary page tables.
@@ -152,6 +157,8 @@ asmlinkage void secondary_start_kernel(void)
 	 */
 	notify_cpu_starting(cpu);
 
+	smp_store_cpu_info(cpu);
+
 	/*
 	 * OK, now it's safe to let the boot CPU continue.  Wait for
 	 * the CPU migration code to notice that the CPU is online
@@ -390,6 +397,10 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 	int err;
 	unsigned int cpu, ncores = num_possible_cpus();
 
+	init_cpu_topology();
+
+	smp_store_cpu_info(smp_processor_id());
+
 	/*
 	 * are we trying to boot more cores than exist?
 	 */
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
new file mode 100644
index 0000000..c1e44d5
--- /dev/null
+++ b/arch/arm64/kernel/topology.c
@@ -0,0 +1,102 @@
+/*
+ * arch/arm64/kernel/topology.c
+ *
+ * Copyright (C) 2011,2013 Linaro Limited.
+ *
+ * Based on the arm32 version written by Vincent Guittot in turn based on
+ * arch/sh/kernel/topology.c
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/cpu.h>
+#include <linux/cpumask.h>
+#include <linux/init.h>
+#include <linux/percpu.h>
+#include <linux/node.h>
+#include <linux/nodemask.h>
+#include <linux/sched.h>
+
+#include <asm/topology.h>
+
+/*
+ * cpu topology table
+ */
+struct cpu_topology cpu_topology[NR_CPUS];
+EXPORT_SYMBOL_GPL(cpu_topology);
+
+const struct cpumask *cpu_coregroup_mask(int cpu)
+{
+	return &cpu_topology[cpu].core_sibling;
+}
+
+static void update_siblings_masks(unsigned int cpuid)
+{
+	struct cpu_topology *cpu_topo, *cpuid_topo = &cpu_topology[cpuid];
+	int cpu;
+
+	/* update core and thread sibling masks */
+	for_each_possible_cpu(cpu) {
+		cpu_topo = &cpu_topology[cpu];
+
+		if (cpuid_topo->cluster_id != cpu_topo->cluster_id)
+			continue;
+
+		cpumask_set_cpu(cpuid, &cpu_topo->core_sibling);
+		if (cpu != cpuid)
+			cpumask_set_cpu(cpu, &cpuid_topo->core_sibling);
+
+		if (cpuid_topo->core_id != cpu_topo->core_id)
+			continue;
+
+		cpumask_set_cpu(cpuid, &cpu_topo->thread_sibling);
+		if (cpu != cpuid)
+			cpumask_set_cpu(cpu, &cpuid_topo->thread_sibling);
+	}
+}
+
+void store_cpu_topology(unsigned int cpuid)
+{
+	struct cpu_topology *cpuid_topo = &cpu_topology[cpuid];
+
+	/* Something should have picked a topology by the time we get here */
+	if (cpuid_topo->core_id == -1)
+		pr_warn("CPU%u: No topology information configured\n", cpuid);
+	else
+		update_siblings_masks(cpuid);
+}
+
+/*
+ * init_cpu_topology is called at boot when only one cpu is running
+ * which prevent simultaneous write access to cpu_topology array
+ */
+void __init init_cpu_topology(void)
+{
+	unsigned int cpu;
+
+	/* init core mask and power*/
+	for_each_possible_cpu(cpu) {
+		struct cpu_topology *cpu_topo = &cpu_topology[cpu];
+
+		cpu_topo->thread_id = -1;
+		cpu_topo->core_id =  -1;
+		cpu_topo->cluster_id = -1;
+		cpumask_clear(&cpu_topo->core_sibling);
+		cpumask_clear(&cpu_topo->thread_sibling);
+	}
+
+	/*
+	 * Assign all remaining CPUs to a cluster so the scheduler
+	 * doesn't get confused.
+	 */
+	for_each_possible_cpu(cpu) {
+		struct cpu_topology *cpu_topo = &cpu_topology[cpu];
+
+		if (cpu_topo->cluster_id == -1) {
+			cpu_topo->cluster_id = INT_MAX;
+			cpu_topo->core_id = cpu;
+		}
+	}
+}
-- 
1.9.0.rc3

[PATCH 1/4] arm64: topology: Implement basic CPU topology support

[Lorenzo Pieralisi]

Hi Mark,

On Tue, Feb 25, 2014 at 04:25:42AM +0000, Mark Brown wrote:
> From: Mark Brown <broonie@linaro.org>
> 
> Add basic CPU topology support to arm64, based on the existing pre-v8
> code and some work done by Mark Hambleton.  This patch does not
> implement any topology discovery support since that should be based on
> information from firmware, it merely implements the scaffolding for
> integration of topology support in the architecture.
> 
> No locking of the topology data is done since it is only modified during
> CPU bringup with external serialisation from the SMP code.
> 
> The goal is to separate the architecture hookup for providing topology
> information from the DT parsing in order to ease review and avoid
> blocking the architecture code (which will be built on by other work)
> with the DT code review by providing something simple and basic.
> 
> A following patch will implement support for parsing the DT topology
> bindings for ARM, similar patches will be needed for ACPI.
> 
> Signed-off-by: Mark Brown <broonie@linaro.org>

I have been clobbering the code with some random dts configs, running on
top of the patch attached (to make code compliant with default if DT
info is missing for some CPUs). Can you give it a go please and run your
tests against it (I have just put it together) ? It should simplify things,
thoughts ?

AFAIK it should be correct, at least the info required by the scheduler
is reset to default (include/linux/topology.h) if DT nodes are
misconfigured. It applies on top of your series.

Thanks,
Lorenzo

-- >8 --
Subject: [PATCH] arm64: kernel: update topology discovery code

If the device tree does not contain topology information for a CPU,
kernel code should set-up topology information for the CPU according
to the default values defined in Documentation/cputopology.txt.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
---
 arch/arm64/kernel/topology.c |   34 +++++++++++++---------------------
 1 files changed, 13 insertions(+), 21 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index e85560a..22ce390 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -317,6 +317,18 @@ static void update_siblings_masks(unsigned int cpuid)
 	struct cpu_topology *cpu_topo, *cpuid_topo = &cpu_topology[cpuid];
 	int cpu;
 
+	if (cpuid_topo->cluster_id == -1) {
+		/*
+		 * DT does not contain topology information for this cpu
+		 * reset it to default behaviour
+		 */
+		pr_warn("CPU%u: No topology information configured\n", cpuid);
+		cpuid_topo->core_id = 0;
+		cpumask_set_cpu(cpuid, &cpuid_topo->core_sibling);
+		cpumask_set_cpu(cpuid, &cpuid_topo->thread_sibling);
+		return;
+	}
+
 	/* update core and thread sibling masks */
 	for_each_possible_cpu(cpu) {
 		cpu_topo = &cpu_topology[cpu];
@@ -339,14 +351,7 @@ static void update_siblings_masks(unsigned int cpuid)
 
 void store_cpu_topology(unsigned int cpuid)
 {
-	struct cpu_topology *cpuid_topo = &cpu_topology[cpuid];
-
-	/* Something should have picked a topology by the time we get here */
-	if (cpuid_topo->core_id == -1)
-		pr_warn("CPU%u: No topology information configured\n", cpuid);
-	else
-		update_siblings_masks(cpuid);
-
+	update_siblings_masks(cpuid);
 	update_cpu_power(cpuid);
 }
 
@@ -372,17 +377,4 @@ void __init init_cpu_topology(void)
 	}
 
 	parse_dt_topology();
-
-	/*
-	 * Assign all remaining CPUs to a cluster so the scheduler
-	 * doesn't get confused.
-	 */
-	for_each_possible_cpu(cpu) {
-		struct cpu_topology *cpu_topo = &cpu_topology[cpu];
-
-		if (cpu_topo->cluster_id == -1) {
-			cpu_topo->cluster_id = INT_MAX;
-			cpu_topo->core_id = cpu;
-		}
-	}
 }
-- 
1.7.5.4

[PATCH 1/4] arm64: topology: Implement basic CPU topology support

[Mark Brown]

On Tue, Feb 25, 2014 at 04:54:11PM +0000, Lorenzo Pieralisi wrote:

> I have been clobbering the code with some random dts configs, running on
> top of the patch attached (to make code compliant with default if DT
> info is missing for some CPUs). Can you give it a go please and run your
> tests against it (I have just put it together) ? It should simplify things,
> thoughts ?

> AFAIK it should be correct, at least the info required by the scheduler
> is reset to default (include/linux/topology.h) if DT nodes are
> misconfigured. It applies on top of your series.

It seems to work fine for me, I'll resend with it squashed in though one
thing below which concerns me a bit.  

Can I suggest that given the sort of thing we're looking at here it
might be easier to apply the code as-is and then do any further work
incrementally?

> If the device tree does not contain topology information for a CPU,
> kernel code should set-up topology information for the CPU according
> to the default values defined in Documentation/cputopology.txt.

> +		pr_warn("CPU%u: No topology information configured\n", cpuid);
> +		cpuid_topo->core_id = 0;

I know this is what the document says and the scheduler copes but it
does make me a bit nervous if we end up with only some CPUs in this
undefined state.  I can't point to any practical problems and it's
going to be the scheduler's fault if it does but I wouldn't be surprised
if there were issues in cases where there is partial topology
information (as opposed to either full topology information or none).

Having said that like I keep saying it seems most sensible to fall back
to MPIDR if we don't have any better idea; it's guaranteed to be
available, may well be correct and helps systems that did a good job
with their hardware.
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[PATCH 1/4] arm64: topology: Implement basic CPU topology support

[Lorenzo Pieralisi]

On Wed, Feb 26, 2014 at 12:50:52AM +0000, Mark Brown wrote:
> On Tue, Feb 25, 2014 at 04:54:11PM +0000, Lorenzo Pieralisi wrote:
> Can I suggest that given the sort of thing we're looking at here it
> might be easier to apply the code as-is and then do any further work
> incrementally?

I think we have enough information to make code complete now, at least
for the topology code, I prefer to merge what's considered to be final.

> > If the device tree does not contain topology information for a CPU,
> > kernel code should set-up topology information for the CPU according
> > to the default values defined in Documentation/cputopology.txt.
> 
> > +		pr_warn("CPU%u: No topology information configured\n", cpuid);
> > +		cpuid_topo->core_id = 0;
> 
> I know this is what the document says and the scheduler copes but it
> does make me a bit nervous if we end up with only some CPUs in this
> undefined state.  I can't point to any practical problems and it's
> going to be the scheduler's fault if it does but I wouldn't be surprised
> if there were issues in cases where there is partial topology
> information (as opposed to either full topology information or none).
> 
> Having said that like I keep saying it seems most sensible to fall back
> to MPIDR if we don't have any better idea; it's guaranteed to be
> available, may well be correct and helps systems that did a good job
> with their hardware.

You have a point. Unless someone feels strongly against this, I would
suggest falling back to MPIDR_EL1 if there is missing or wrong information in
DT.

To do that, you need to scrap the structures initialized from DT
altogether if there is missing or wrong DT information, it is either DT for
all CPUs or MPIDR_EL1 for all CPUs, we can't mix the approaches (and while
at it I'd rather parse the HW MPIDR_EL1 so that you get get the MT bit
from it, which is not present in cpu_logical_map).

Let's sum it up:

- if there is a cpu-map, it takes precedence. If there are missing bits
  of info in the cpu-map we WARN_ON (since this is a firmware bug,
  cpu-map overrides MPIDR_EL1 registers info, if the information in cpu-map
  is wrong or missing we should flag it up and that deserves a WARN_ON)
- if cpu-map is missing, we fall back to MPIDR_EL1 and print a message
  just describing that.

I noticed you will have to add some macros to read MPIDR_EL1 bits in the
process.

Thanks,
Lorenzo

[PATCH 1/4] arm64: topology: Implement basic CPU topology support

[Mark Brown]

On Wed, Feb 26, 2014 at 12:32:08PM +0000, Lorenzo Pieralisi wrote:
> On Wed, Feb 26, 2014 at 12:50:52AM +0000, Mark Brown wrote:

> > Can I suggest that given the sort of thing we're looking at here it
> > might be easier to apply the code as-is and then do any further work
> > incrementally?

> I think we have enough information to make code complete now, at least
> for the topology code, I prefer to merge what's considered to be final.

Hrm, in that case perhaps the first patch is OK to go?  The changes
still being discussed are to the DT binding handling and the addition of
a new parsing mechanism (for MPIDR, which I'd do as a separate patch).
This would be quite helpful, tweaks to the first patch typically cause
manual rebases against the DT patches which increases the stop energy.

> > Having said that like I keep saying it seems most sensible to fall back
> > to MPIDR if we don't have any better idea; it's guaranteed to be
> > available, may well be correct and helps systems that did a good job
> > with their hardware.

> You have a point. Unless someone feels strongly against this, I would
> suggest falling back to MPIDR_EL1 if there is missing or wrong information in
> DT.

Catalin seemed very concerned about any use at all of MPIDR, that's why
the code was removed originally.  Catalin?
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[PATCH 1/4] arm64: topology: Implement basic CPU topology support

[Catalin Marinas]

On Wed, Feb 26, 2014 at 02:46:10PM +0000, Mark Brown wrote:
> On Wed, Feb 26, 2014 at 12:32:08PM +0000, Lorenzo Pieralisi wrote:
> > On Wed, Feb 26, 2014 at 12:50:52AM +0000, Mark Brown wrote:
> > > Having said that like I keep saying it seems most sensible to fall back
> > > to MPIDR if we don't have any better idea; it's guaranteed to be
> > > available, may well be correct and helps systems that did a good job
> > > with their hardware.
> 
> > You have a point. Unless someone feels strongly against this, I would
> > suggest falling back to MPIDR_EL1 if there is missing or wrong information in
> > DT.
> 
> Catalin seemed very concerned about any use at all of MPIDR, that's why
> the code was removed originally.  Catalin?

My concern is that the MPIDR is just considered a unique ID. The ARMv8
relaxes the requirement so that it no longer needs to start at 0 and
increase monotonically. I checked with the architecture guys here and
they still expect the affinity hierarchy to be described by MPIDR but we
can have holes in the range for certain levels (i.e. an affinity level
may not start at 0 and may not even increase monotonically for
subsequent CPUs).

So we can either add a tolerant MPIDR parsing or we simply assume that
the topology is _flat_ when DT doesn't provide the information.

-- 
Catalin

[PATCH 1/4] arm64: topology: Implement basic CPU topology support

[Lorenzo Pieralisi]

On Wed, Feb 26, 2014 at 03:48:58PM +0000, Catalin Marinas wrote:
> On Wed, Feb 26, 2014 at 02:46:10PM +0000, Mark Brown wrote:
> > On Wed, Feb 26, 2014 at 12:32:08PM +0000, Lorenzo Pieralisi wrote:
> > > On Wed, Feb 26, 2014 at 12:50:52AM +0000, Mark Brown wrote:
> > > > Having said that like I keep saying it seems most sensible to fall back
> > > > to MPIDR if we don't have any better idea; it's guaranteed to be
> > > > available, may well be correct and helps systems that did a good job
> > > > with their hardware.
> > 
> > > You have a point. Unless someone feels strongly against this, I would
> > > suggest falling back to MPIDR_EL1 if there is missing or wrong information in
> > > DT.
> > 
> > Catalin seemed very concerned about any use at all of MPIDR, that's why
> > the code was removed originally.  Catalin?
> 
> My concern is that the MPIDR is just considered a unique ID. The ARMv8
> relaxes the requirement so that it no longer needs to start at 0 and
> increase monotonically. I checked with the architecture guys here and
> they still expect the affinity hierarchy to be described by MPIDR but we
> can have holes in the range for certain levels (i.e. an affinity level
> may not start at 0 and may not even increase monotonically for
> subsequent CPUs).
> 
> So we can either add a tolerant MPIDR parsing or we simply assume that
> the topology is _flat_ when DT doesn't provide the information.

I think that as far as the topology structures are concerned we can fall
back to MPIDR_EL1 in case cpu-map is missing or incomplete, since even
if the affinity levels contain holes or are not sequential that should
be fine (but see below). After all we have cpu-map to correct things for
this same reason and that will take precedence over the MPIDR_EL1 anyway.

Macros below are required for the scheduler to work. The ids are arch
dependent (so generic code cannot rely on them being sequential or
follow any rule) and if we fall back to MPIDR_EL1 they will get initialized.

#define topology_physical_package_id(cpu)	(cpu_topology[cpu].socket_id)
#define topology_core_id(cpu)		(cpu_topology[cpu].core_id)
#define topology_core_cpumask(cpu)	(&cpu_topology[cpu].core_sibling)
#define topology_thread_cpumask(cpu)	(&cpu_topology[cpu].thread_sibling)

#define mc_capable()	(cpu_topology[0].socket_id != -1)
#define smt_capable()	(cpu_topology[0].thread_id != -1)

What would be wrong, is leaving the core_sibling and thread_sibling
masks empty and this CAN happen even on current arm32 code if the
cluster id field (ie MPIDR[15:8] for the sake of this discussion) is
different for different CPUs, and that's a bug that fortunately was
never hit (it is a totally valid MPIDR layout, a bit weird though).

On an arm32 4 cpus system with MPIDR layout {0x100, 0x200, 0x300, 0x400}
(which is allowed) the kernel would panic (since the thread_sibling and
core_sibling masks would end up empty).

So I agree with Catalin, either we allow a fall-back to MPIDR_EL1, with relaxed
parsing rules (but let's not forget what I wrote above), or we keep the
current set but with following changes:

- if s topology node for a cpu (or some cpus) is missing or wrong, the whole
  topology structure should be reverted to default (as in
  include/linux/topology.h Documentation/cputopology.txt). This solves Mark's
  concern about having some cpus with missing topology information.
  NB: My patch does not do that, it resets topology only for the misconfigured
  cpu.

That's the best we can do. I think that an MPIDR_EL1 fall back mechanism
should be put in place, as a separate patch or squashed to patch 1.

I would prefer the latter, but if you want to get the infrastructure in
first I think that's acceptable.

Apologies for all requested changes.

Thanks,
Lorenzo

[PATCH 1/4] arm64: topology: Implement basic CPU topology support

[Mark Brown]

On Wed, Feb 26, 2014 at 05:50:04PM +0000, Lorenzo Pieralisi wrote:

> What would be wrong, is leaving the core_sibling and thread_sibling
> masks empty and this CAN happen even on current arm32 code if the
> cluster id field (ie MPIDR[15:8] for the sake of this discussion) is
> different for different CPUs, and that's a bug that fortunately was
> never hit (it is a totally valid MPIDR layout, a bit weird though).

This is a good point, I will make sure any MPIDR code handles it (we
should fix the 32 bit code as well of course, I'll try to look at that
too).

> - if s topology node for a cpu (or some cpus) is missing or wrong, the whole
>   topology structure should be reverted to default (as in
>   include/linux/topology.h Documentation/cputopology.txt). This solves Mark's
>   concern about having some cpus with missing topology information.
>   NB: My patch does not do that, it resets topology only for the misconfigured
>   cpu.

I would certainly prefer this, I'll do an update (though not today,
trains again).

> That's the best we can do. I think that an MPIDR_EL1 fall back mechanism
> should be put in place, as a separate patch or squashed to patch 1.

> I would prefer the latter, but if you want to get the infrastructure in
> first I think that's acceptable.

I'd certainly prefer to get the code merged and work incrementally, it'd
make life easier to avoid having to manage the rebases.
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[PATCH 1/4] arm64: topology: Implement basic CPU topology support

[Mark Brown]

On Wed, Feb 26, 2014 at 03:48:58PM +0000, Catalin Marinas wrote:

> My concern is that the MPIDR is just considered a unique ID. The ARMv8
> relaxes the requirement so that it no longer needs to start at 0 and
> increase monotonically. I checked with the architecture guys here and
> they still expect the affinity hierarchy to be described by MPIDR but we
> can have holes in the range for certain levels (i.e. an affinity level
> may not start at 0 and may not even increase monotonically for
> subsequent CPUs).

I don't think anything has a problem with holes in the number range, the
only thing I can think of which imposes that requirement is the DT
binding but obviously that's not relevant if we are using MPIDR.  The
core topology documentation explicitly says that these are physical IDs
and entirely up to the architecture/platform.  It'd seem odd given that
we have hotplug support.

What problems do you anticipate?

> So we can either add a tolerant MPIDR parsing or we simply assume that
> the topology is _flat_ when DT doesn't provide the information.

Right, that's what the current code does but I'm not sure it's the best
option.
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[PATCH 2/4] arm64: topology: Add support for topology DT bindings

[Mark Brown]

From: Mark Brown <broonie@linaro.org>

Add support for parsing the explicit topology bindings to discover the
topology of the system.

Since it is not currently clear how to map multi-level clusters for the
scheduler all leaf clusters are presented to the scheduler at the same
level. This should be enough to provide good support for current systems.

Signed-off-by: Mark Brown <broonie@linaro.org>
---
 arch/arm64/kernel/topology.c | 142 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 142 insertions(+)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index c1e44d5..cda9a48 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -17,10 +17,150 @@
 #include <linux/percpu.h>
 #include <linux/node.h>
 #include <linux/nodemask.h>
+#include <linux/of.h>
 #include <linux/sched.h>
 
 #include <asm/topology.h>
 
+#ifdef CONFIG_OF
+static int __init get_cpu_for_node(struct device_node *node)
+{
+	struct device_node *cpu_node;
+	int cpu;
+
+	cpu_node = of_parse_phandle(node, "cpu", 0);
+	if (!cpu_node)
+		return -1;
+
+	for_each_possible_cpu(cpu) {
+		if (of_get_cpu_node(cpu, NULL) == cpu_node)
+			return cpu;
+	}
+
+	pr_crit("Unable to find CPU node for %s\n", cpu_node->full_name);
+	return -1;
+}
+
+static void __init parse_core(struct device_node *core, int cluster_id,
+			      int core_id)
+{
+	char name[10];
+	bool leaf = true;
+	int i = 0;
+	int cpu;
+	struct device_node *t;
+
+	do {
+		snprintf(name, sizeof(name), "thread%d", i);
+		t = of_get_child_by_name(core, name);
+		if (t) {
+			leaf = false;
+			cpu = get_cpu_for_node(t);
+			if (cpu >= 0) {
+				cpu_topology[cpu].cluster_id = cluster_id;
+				cpu_topology[cpu].core_id = core_id;
+				cpu_topology[cpu].thread_id = i;
+			} else {
+				pr_err("%s: Can't get CPU for thread\n",
+				       t->full_name);
+			}
+		}
+		i++;
+	} while (t);
+
+	cpu = get_cpu_for_node(core);
+	if (cpu >= 0) {
+		if (!leaf) {
+			pr_err("%s: Core has both threads and CPU\n",
+			       core->full_name);
+			return;
+		}
+
+		cpu_topology[cpu].cluster_id = cluster_id;
+		cpu_topology[cpu].core_id = core_id;
+	} else if (leaf) {
+		pr_err("%s: Can't get CPU for leaf core\n", core->full_name);
+	}
+}
+
+static void __init parse_cluster(struct device_node *cluster, int depth)
+{
+	char name[10];
+	bool leaf = true;
+	bool has_cores = false;
+	struct device_node *c;
+	static int __initdata cluster_id;
+	int core_id = 0;
+	int i;
+
+	/*
+	 * First check for child clusters; we currently ignore any
+	 * information about the nesting of clusters and present the
+	 * scheduler with a flat list of them.
+	 */
+	i = 0;
+	do {
+		snprintf(name, sizeof(name), "cluster%d", i);
+		c = of_get_child_by_name(cluster, name);
+		if (c) {
+			parse_cluster(c, depth + 1);
+			leaf = false;
+		}
+		i++;
+	} while (c);
+
+	/* Now check for cores */
+	i = 0;
+	do {
+		snprintf(name, sizeof(name), "core%d", i);
+		c = of_get_child_by_name(cluster, name);
+		if (c) {
+			has_cores = true;
+
+			if (depth == 0)
+				pr_err("%s: cpu-map children should be clusters\n",
+				       c->full_name);
+
+			if (leaf)
+				parse_core(c, cluster_id, core_id++);
+			else
+				pr_err("%s: Non-leaf cluster with core %s\n",
+				       cluster->full_name, name);
+		}
+		i++;
+	} while (c);
+
+	if (leaf && !has_cores)
+		pr_warn("%s: empty cluster\n", cluster->full_name);
+
+	if (leaf)
+		cluster_id++;
+}
+
+static void __init parse_dt_topology(void)
+{
+	struct device_node *cn;
+
+	cn = of_find_node_by_path("/cpus");
+	if (!cn) {
+		pr_err("No CPU information found in DT\n");
+		return;
+	}
+
+	/*
+	 * When topology is provided cpu-map is essentially a root
+	 * cluster with restricted subnodes.
+	 */
+	cn = of_find_node_by_name(cn, "cpu-map");
+	if (!cn)
+		return;
+	parse_cluster(cn, 0);
+}
+
+#else
+static inline void parse_dt_topology(void) {}
+#endif
+
 /*
  * cpu topology table
  */
@@ -87,6 +227,8 @@ void __init init_cpu_topology(void)
 		cpumask_clear(&cpu_topo->thread_sibling);
 	}
 
+	parse_dt_topology();
+
 	/*
 	 * Assign all remaining CPUs to a cluster so the scheduler
 	 * doesn't get confused.
-- 
1.9.0.rc3

[PATCH 3/4] arm64: topology: Tell the scheduler about the relative power of cores

[Mark Brown]

From: Mark Brown <broonie@linaro.org>

In heterogeneous systems like big.LITTLE systems the scheduler will be
able to make better use of the available cores if we provide power numbers
to it indicating their relative performance. Do this by parsing the CPU
nodes in the DT.

This code currently has no effect as no information on the relative
performance of the cores is provided.

Signed-off-by: Mark Brown <broonie@linaro.org>
---
 arch/arm64/kernel/topology.c | 142 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 142 insertions(+)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index cda9a48..b330e79 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -19,9 +19,33 @@
 #include <linux/nodemask.h>
 #include <linux/of.h>
 #include <linux/sched.h>
+#include <linux/slab.h>
 
 #include <asm/topology.h>
 
+/*
+ * cpu power table
+ * This per cpu data structure describes the relative capacity of each core.
+ * On a heteregenous system, cores don't have the same computation capacity
+ * and we reflect that difference in the cpu_power field so the scheduler can
+ * take this difference into account during load balance. A per cpu structure
+ * is preferred because each CPU updates its own cpu_power field during the
+ * load balance except for idle cores. One idle core is selected to run the
+ * rebalance_domains for all idle cores and the cpu_power can be updated
+ * during this sequence.
+ */
+static DEFINE_PER_CPU(unsigned long, cpu_scale);
+
+unsigned long arch_scale_freq_power(struct sched_domain *sd, int cpu)
+{
+	return per_cpu(cpu_scale, cpu);
+}
+
+static void set_power_scale(unsigned int cpu, unsigned long power)
+{
+	per_cpu(cpu_scale, cpu) = power;
+}
+
 #ifdef CONFIG_OF
 static int __init get_cpu_for_node(struct device_node *node)
 {
@@ -137,9 +161,49 @@ static void __init parse_cluster(struct device_node *cluster, int depth)
 		cluster_id++;
 }
 
+struct cpu_efficiency {
+	const char *compatible;
+	unsigned long efficiency;
+};
+
+/*
+ * Table of relative efficiency of each processors
+ * The efficiency value must fit in 20bit and the final
+ * cpu_scale value must be in the range
+ *   0 < cpu_scale < 3*SCHED_POWER_SCALE/2
+ * in order to return@most 1 when DIV_ROUND_CLOSEST
+ * is used to compute the capacity of a CPU.
+ * Processors that are not defined in the table,
+ * use the default SCHED_POWER_SCALE value for cpu_scale.
+ */
+static const struct cpu_efficiency table_efficiency[] = {
+	{ NULL, },
+};
+
+static unsigned long *__cpu_capacity;
+#define cpu_capacity(cpu)	__cpu_capacity[cpu]
+
+static unsigned long middle_capacity = 1;
+
+/*
+ * Iterate all CPUs' descriptor in DT and compute the efficiency
+ * (as per table_efficiency). Also calculate a middle efficiency
+ * as close as possible to  (max{eff_i} - min{eff_i}) / 2
+ * This is later used to scale the cpu_power field such that an
+ * 'average' CPU is of middle power. Also see the comments near
+ * table_efficiency[] and update_cpu_power().
+ */
 static void __init parse_dt_topology(void)
 {
+	const struct cpu_efficiency *cpu_eff;
 	struct device_node *cn;
+	unsigned long min_capacity = ULONG_MAX;
+	unsigned long max_capacity = 0;
+	unsigned long capacity = 0;
+	int cpu;
+
+	__cpu_capacity = kcalloc(nr_cpu_ids, sizeof(*__cpu_capacity),
+				 GFP_NOWAIT);
 
 	cn = of_find_node_by_path("/cpus");
 	if (!cn) {
@@ -155,10 +219,84 @@ static void __init parse_dt_topology(void)
 	if (!cn)
 		return;
 	parse_cluster(cn, 0);
+
+	for_each_possible_cpu(cpu) {
+		const u32 *rate;
+		int len;
+
+		/* Too early to use cpu->of_node */
+		cn = of_get_cpu_node(cpu, NULL);
+		if (!cn) {
+			pr_err("Missing device node for CPU %d\n", cpu);
+			continue;
+		}
+
+		for (cpu_eff = table_efficiency; cpu_eff->compatible; cpu_eff++)
+			if (of_device_is_compatible(cn, cpu_eff->compatible))
+				break;
+
+		if (cpu_eff->compatible == NULL) {
+			pr_warn("%s: Unknown CPU type\n", cn->full_name);
+			continue;
+		}
+
+		rate = of_get_property(cn, "clock-frequency", &len);
+		if (!rate || len != 4) {
+			pr_err("%s: Missing clock-frequency property\n",
+				cn->full_name);
+			continue;
+		}
+
+		capacity = ((be32_to_cpup(rate)) >> 20) * cpu_eff->efficiency;
+
+		/* Save min capacity of the system */
+		if (capacity < min_capacity)
+			min_capacity = capacity;
+
+		/* Save max capacity of the system */
+		if (capacity > max_capacity)
+			max_capacity = capacity;
+
+		cpu_capacity(cpu) = capacity;
+	}
+
+	/* If min and max capacities are equal we bypass the update of the
+	 * cpu_scale because all CPUs have the same capacity. Otherwise, we
+	 * compute a middle_capacity factor that will ensure that the capacity
+	 * of an 'average' CPU of the system will be as close as possible to
+	 * SCHED_POWER_SCALE, which is the default value, but with the
+	 * constraint explained near table_efficiency[].
+	 */
+	if (min_capacity == max_capacity)
+		return;
+	else if (4 * max_capacity < (3 * (max_capacity + min_capacity)))
+		middle_capacity = (min_capacity + max_capacity)
+				>> (SCHED_POWER_SHIFT+1);
+	else
+		middle_capacity = ((max_capacity / 3)
+				>> (SCHED_POWER_SHIFT-1)) + 1;
+
+}
+
+/*
+ * Look for a customed capacity of a CPU in the cpu_topo_data table during the
+ * boot. The update of all CPUs is in O(n^2) for heteregeneous system but the
+ * function returns directly for SMP system.
+ */
+static void update_cpu_power(unsigned int cpu)
+{
+	if (!cpu_capacity(cpu))
+		return;
+
+	set_power_scale(cpu, cpu_capacity(cpu) / middle_capacity);
+
+	pr_info("CPU%u: update cpu_power %lu\n",
+		cpu, arch_scale_freq_power(NULL, cpu));
 }
 
 #else
 static inline void parse_dt_topology(void) {}
+static inline void update_cpu_power(unsigned int cpuid) {}
 #endif
 
 /*
@@ -206,6 +344,8 @@ void store_cpu_topology(unsigned int cpuid)
 		pr_warn("CPU%u: No topology information configured\n", cpuid);
 	else
 		update_siblings_masks(cpuid);
+
+	update_cpu_power(cpuid);
 }
 
 /*
@@ -225,6 +365,8 @@ void __init init_cpu_topology(void)
 		cpu_topo->cluster_id = -1;
 		cpumask_clear(&cpu_topo->core_sibling);
 		cpumask_clear(&cpu_topo->thread_sibling);
+
+		set_power_scale(cpu, SCHED_POWER_SCALE);
 	}
 
 	parse_dt_topology();
-- 
1.9.0.rc3

[PATCH 4/4] arm64: topology: Provide relative power numbers for cores

[Mark Brown]

From: Mark Brown <broonie@linaro.org>

Provide performance numbers to the scheduler to help it fill the cores in
the system on big.LITTLE systems. With the current scheduler this may
perform poorly for applications that try to do OpenMP style work over all
cores but should help for more common workloads. The current 32 bit ARM
implementation provides a similar estimate so this helps ensure that
work to improve big.LITTLE systems on ARMv7 systems performs similarly
on ARMv8 systems.

The power numbers are the same as for ARMv7 since it seems that the
expected differential between the big and little cores is very similar on
both ARMv7 and ARMv8.  In both ARMv7 and ARMv8 cases the numbers were
based on the published DMIPS numbers.

These numbers are just an initial and basic approximation for use with
the current scheduler, it is likely that both experience with silicon
and ongoing work on improving the scheduler will lead to further tuning
or will tune automatically at runtime and so make the specific choice of
numbers here less critical.

Signed-off-by: Mark Brown <broonie@linaro.org>
---
 arch/arm64/kernel/topology.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index b330e79..e85560a 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -177,6 +177,8 @@ struct cpu_efficiency {
  * use the default SCHED_POWER_SCALE value for cpu_scale.
  */
 static const struct cpu_efficiency table_efficiency[] = {
+	{ "arm,cortex-a57", 3891 },
+	{ "arm,cortex-a53", 2048 },
 	{ NULL, },
 };
 
-- 
1.9.0.rc3